Switching regulator input current sensing circuit, system, and method

ABSTRACT

A Buck switching regulator includes first Buck switching regulator circuitry is operable to generate a first output voltage from an input voltage and operable to generate a first sensed voltage having a value that is proportional to an output current being provided by the first Buck switching regulator circuitry. The first Buck switching regulator circuitry receives an input current and operates at a first duty cycle determined by a duty cycle signal. Input current sensing circuitry includes second Buck switching regulator circuitry coupled to the first Buck regulator switching circuitry to receive the duty cycle signal and to receive the first sensed voltage as an input voltage to the second Buck switching regulator circuitry. The second Buck switching regulator circuitry is operable responsive to the duty cycle signal to generate a second output voltage from the first sensed voltage. The second output voltage has a value that is proportional to the input current being supplied to the first Buck switching regulator circuitry. Such a Buck switching regulator can be utilized in a variety of different types of electronic systems, such as laptop computer systems, and can also be used in charging systems in laptop computer and other types of electronic systems.

PRIORITY CLAIM

The present application claims the benefit of U.S. Provisional PatentApplication No. 61/092,650, filed Aug. 28, 2008, which application isincorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments of the present invention are directed generally to switchingregulators and more specifically to circuits and methods for determiningthe efficiency of such switching regulators so that this efficiency maythen be used in controlling the operation of the switching regulator.

BACKGROUND OF THE INVENTION

A typical switching regulator converts a voltage from one level toanother by controlling a switching element or elements to alternatelystore and release energy in an energy storage element, such as aninductive element. In operation, energy from an input power source isalternately stored in the inductive element and then released from theinductive element to thereby supply power to a load being driven. Manydifferent topologies exist for switching regulators and may be generallyclassified as either step-up converters or step-down converters.Examples of step-up converters providing an output voltage Vout that isgreater than a supplied input voltage Vin include Buck-boost and singleended primary inductor converters (SEPICs). Conversely, a Buck converteris an example of a step-down converter that provides an output voltageVout that is less than the input voltage Vin.

In switching regulators, it is often desirable to measure an inputcurrent Iin coming into or being supplied from an input power source tothe regulator during operation. This is particularly true when batteriesare being used as the input power source and the amount of dischargecurrent out of the batteries needs to be monitored and/or limited to,for example, extend the life of the batteries. Moreover, customers oftenhave the need or desire to determine the power efficiency of theirswitching regulators, and to do so requires the ability to monitor theinput voltage Vin and input current Iin supplied to the switchingregulator along with the output voltage Vout and output current Ioutprovided by the regulator.

The power efficiency of a switching regulator is given by the outputpower Pout provided by the regulator divided by the input power Pinsupplied to the regulator (Pout/Pin), where Pout=Iout×Vout andPin=Iin×Vin. While customers would like to be able to determine powerefficiency, they do not want to significantly increase the cost orcomplexity of their regulators to do so. Input voltage Vin, outputvoltage Vout and output current Iout are all presently monitored in mostswitching regulators, primarily because these parameters are easilymeasured and useful or required for controlling operation of theregulator. Input current Iin, however, is not typically monitored andneeds to be in order to enable the power efficiency to be determined.The input current Iin to a switching regulator is a pulsed current not adirect current (DC) signal and accordingly is not easily measured, aswill be appreciated by those skilled in the art. For the input currentIin an average value must be determined for use in calculating powerefficiency with this average value being based upon the magnitude andduty cycle of the input current. This additional circuitry increases thecomplexity of circuitry forming the switching regulator, occupiesvaluable space in an integrated circuit in which the switching regulatoror portions thereof are typically formed, and increases the cost of theregulator.

Alternative circuits and methods are needed for the input and outputcurrent and voltage measurements such that overall efficiency of aswitching regulator can be determined.

SUMMARY

According to one embodiment of the present invention, a Buck switchingregulator includes first Buck switching regulator circuitry is operableto generate a first output voltage from an input voltage and operable togenerate a first sensed voltage having a value that is proportional toan output current being provided by the first Buck switching regulatorcircuitry. The first Buck switching regulator circuitry receives aninput current and operates at a first duty cycle determined by a dutycycle signal. Input current sensing circuitry includes second Buckswitching regulator circuitry coupled to the first Buck regulatorswitching circuitry to receive the duty cycle signal and to receive thefirst sensed voltage as an input voltage to the second Buck switchingregulator circuitry. The second Buck switching regulator circuitry isoperable responsive to the duty cycle signal to generate a second outputvoltage from the first sensed voltage. The second output voltage has avalue that is proportional to the input current being supplied to thefirst Buck switching regulator circuitry. Such a Buck switchingregulator can be utilized in a variety of different types of electronicsystems, such as laptop computer systems, and can also be used incharging systems in laptop computer and other types of electronicsystems.

According to another embodiment of the present invention, a method ofsensing the input current being supplied to a first Buck switchingregulator includes controlling the first Buck switching regulator at afirst duty cycle to generate a first voltage having a value indicatingthe value of an output current being provided by the first Buckswitching regulator, providing the first voltage as an input voltage toa second Buck switching regulator, and controlling the second Buckswitching regulator at the first duty cycle to generate a second outputvoltage, the second output voltage having a value that is proportionalto the value of the input current being supplied to the first Buckswitching regulator.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a functional block diagram of a Buck switching regulatorincluding an input current sensing circuit according to an embodiment ofthe present invention.

FIG. 2 is a more detailed functional block diagram and schematic of theBuck switching regulator of FIG. 1 according to one embodiment of thepresent invention.

FIG. 3 is functional block diagram and schematic of another embodimentof the Buck switching regulator including components for implementingthe regulator circuitry in an integrated circuit.

FIG. 4 is a more detailed functional block diagram and schematic of theBuck switching regulator of FIG. 1 according to another embodiment ofthe present invention.

FIG. 5 is functional block diagram and schematic of a charging controlsystem including the Buck switching regulator and input current sensingcircuit of FIGS. 1-3 according to another embodiment of the presentinvention.

FIG. 6 is a functional block diagram of an electronic system includingthe Buck switching regulator of FIGS. 1-4 and/or battery chargingcontrol system of FIG. 5 according to another embodiment of the presentinvention.

DETAILED DESCRIPTION

FIG. 1 is a functional block diagram of a Buck switching regulator 100including an input current sensing circuit 102 for calculating an inputcurrent Iin being supplied to a primary or first Buck switchingregulator circuit 104 according to an embodiment of the presentinvention. The first Buck switching regulator circuit 104 generates afirst output voltage Vout and an output current Iout from an inputvoltage Vin and input current Iin, with the output voltage and currentbeing supplied to drive a load L. In operation, the first Buck switchingregulator circuit 104 operates at a duty cycle to generate the desiredfirst output voltage Vout, and generates duty cycle signals DCYC havingON/OFF times indicating the duty cycle at which the Buck switchingregulator circuit 104 is operating. In addition, the first Buckswitching regulator circuit 104 generates a first sensed voltageV_(IOUT) having a value that indicates the value of the output currentIout the first Buck switching regulator circuit is supplying to the loadL. In response to the duty cycle signals DCYC and first sensed outputvoltage V_(IOUT), the input current sensing circuit 102 generates asecond output voltage V_(IIN) having a value that indicates the value ofthe input current Iin being supplied to the Buck switching regulatorcircuit 104.

The input current sensing circuit 102 utilizes only the duty cyclesignal DCYC and first sensed output voltage V_(IOUT) of the first Buckswitching regulator circuit 104 to generate the second output voltageV_(IIN) that is proportional to the input current Iin being supplied tothe first Buck switching regulator. With the input current sensingcircuit 102 there are no separate components required for directlysensing the input current Iin. While the separate input current sensingcircuit 102 is required to sense the input current Iin, relativelysimple circuitry forms the input current sensing circuit according toembodiments of the present invention. This reduces the size, complexityand thus overall cost of the Buck switching regulator 100.

Even though various embodiments and advantages of the present inventionare set forth in the following description, the present disclosure isillustrative only, and changes may be made in detail and yet remainwithin the broad principles of the present invention. Therefore, thepresent invention is to be limited only by the appended claims.Furthermore, in the present description certain details have been setforth in conjunction with the described embodiments of the presentinvention to provide a sufficient understanding of the invention. Oneskilled in the art will appreciate, however, that the invention itselfand various aspects thereof may be practiced without these particulardetails. Furthermore, one skilled in the art will appreciate that thesample embodiments described do not limit the scope of the presentinvention, and will also understand that various modifications,equivalents, and combinations of the disclosed embodiments andcomponents of such embodiments are within the scope of the presentinvention. Embodiments including fewer than all the components of any ofthe respective described embodiments may also be within the scope of thepresent invention although not expressly described in detail herein.Finally, the operation or structure of well known components and/orprocesses has not been shown or described in detail herein to avoidunnecessarily obscuring the present invention.

FIG. 2 is a more detailed functional block diagram and schematic of theBuck switching regulator 100 of FIG. 1 according to one embodiment ofthe present invention. In this embodiment, the first Buck switchingregulator circuit 104 includes a first power switch PS1 and a diode Dconnected in series between the input power source (not shown) supplyingthe input voltage Vin and input current Iin and a ground referenceplane. The power switch PS1 is a power MOSFET in the example of FIG. 2,although different types of transistors and switching circuits may beutilized in other embodiments. A control circuit 200 applies a gatingsignal G to control the turning ON/OFF of the power switch PS1. The dutycycle D of the gating signal G defines the duty cycle at which the firstBuck switching regulator circuit 104 operates. A first phase node PH1 isdefined at the interconnection of the power switch PS1 and the diode D,with the voltage on this node varying as the power switch PS1 isalternately turned ON and OFF responsive to the gating signal G.

When the control circuit 200 activates the G to turn ON the power switchPS1, magnetic energy is stored in a first conductor L1 connected inseries with a sense resistor RS between the first phase node PH1 and afirst output node OUT1 on which the output voltage Vout is generated.Conversely, when the control circuit 200 deactivates the gating signal Gto turn OFF the power switch PS1, magnetic energy is released from thefirst conductor L1 via a current flowing through the diode D. A sensevoltage Vs develops across the sense resistor RS in response to theoutput current Iout flowing through the sense resistor and into a load(not shown in FIG. 2) connected to the output node OUT1 of the firstBuck switching regulator circuit 104. The sense voltage Vs is appliedthrough a filter network formed by resistors R1, R2 and a capacitor C1to an amplifier 202 having a gain A. The amplifier 202 generates a firstsensed voltage V_(IOUT) having a value that is proportional to the valueof the output current Iout flowing through the sense resistor Rs. Acapacitor C2 is connected between the output node OUT1 and groundreference plane and functions to filter the output voltage Voutgenerated on the output node.

As seen in FIG. 2 a phase signal PHS on the phase node PH1 and outputvoltage Vout on the output node OUT1 collectively form the duty cyclesignal DCYC (see FIG. 1) that is applied to the input current sensingcircuit 102. More specifically, the phase signal PHS is applied to afirst input of a first comparator 204 while the output voltage Vout onthe node OUT1 is coupled through a first voltage divider formed byresistors R3 and R4 to provide a first reference voltage on a secondinput of the comparator. Similarly, the output voltage Vout on the nodeOUT1 is coupled through a second voltage divider formed by resistors R5and R6 to provide a second reference voltage on a first input of asecond comparator 206 and the phase signal PHS is applied to a secondinput of the second comparator 204.

In response to the PHS signal and output voltage Vout, the first andsecond comparators 204 and 206 generate a phase-high signal PH-HI andphase-low signal PH-LO, respectively. Note that the duty cycle D of thegating signal G defines the duty cycle of the first Buck switchingregulator circuit 104 and that the duty cycle signal DCYC formed by thePHS signal and the output voltage Vout also indicate the duty cycle D ofthe first Buck switching regulator circuit 104. Two power switches PS2and PS3 in the input current sensing circuit 102 are connected in seriesbetween the output of the amplifier 202 and a ground reference plane andare alternately activated and deactivated responsive to the PH-HI andPH-LO signals. The PH-HI and PH-LO signals are complementary signals andthus when the PH-HI signal is activated, turning ON the power switchPS2, the PH-LO signal is deactivated, turning OFF the power switch PS3.Conversely, when the PH-HI signal is deactivated, turning OFF the powerswitch PS2, the PH-LO signal is activated, turning ON the power switchPS3.

A second phase node PH2 is formed at the interconnection of the powerswitches PS2 and PS3 and a second conductor L2 and resistor R7 areconnected in series between the second phase node and a second outputnode OUT2 of the input current sensing circuit 102. A capacitor C3 andthe resistor R7 form a low pass filter that filters the signal from theinductor L2 to generate a second output voltage V_(IIN) on the secondoutput node OUT2, with the second output voltage having a value that isproportional to the input current Iin being supplied to the first Buckswitching regulator circuit 104, as previously mentioned above and aswill be described in more detail below. The second output voltageV_(IIN) is applied to the control circuit 200 in the first Buckswitching regulator circuit 104, and the control circuit utilizes thesecond output voltage along with the first sensed voltage V_(IOUT) fromthe amplifier 202 and the output voltage Vout on the output node OUT1 incontrolling the overall operation of the Buck switching regulatorcircuit, as will now be explained in more detail.

In operation of the Buck switching regulator 100, the control circuit200 in the first Buck switching regulator circuit 104 controls theoperation of the Buck switching regulator circuit responsive to theinput voltage Vin, output voltage Vout, and the voltages V_(IIN) andV_(IOUT) to generate the desired values for the output voltage Vout andoutput current Iout. Note that the first sensed voltage V_(IOUT) has avalue that is proportional to the value of the output current Iout whilethe second output voltage V_(IIN) has a value proportional to the inputcurrent Iin. As a result, the control circuit 200 of the first Buckswitching regulator circuit 104 receives information about the inputcurrent Iin, input voltage Vin, output current Iout, and output voltageVout of the Buck switching regulator circuit and can thus utilize thisinformation in determining the efficiency of the Buck switchingregulator circuit.

The control circuit 200 can utilize the information about the inputcurrent Iin from the second output voltage V_(IIN) to limit the value ofthe input current being supplied to the first Buck switching regulatorcircuit 104. In addition, the control circuit 200 can utilize thedetermined efficiency to control the overall operation of the first Buckswitching regulator circuit 104 to improve the efficiency of the Buckswitching regulator circuit and thereby reduce the power consumption ofthe overall Buck switching regulator 100. The control circuit 200 canalso provide efficiency information to external circuitry (not shown)containing or coupled to the Buck switching regulator 100 and suchexternal circuitry could, for example, utilize this efficiencyinformation in controlling the overall operation of a system of whichthe external circuitry and a switching regulator are a part.

Note that one skilled in the art will understand the theory andoperation of the first Buck switching regulator circuit 1014 and thus,for the sake of brevity, its detailed operation will not be described inmore detail herein. The general theory and operation of Buck switchingregulator circuits will, however, be described below in detail withregarding to discussing the operation of the input current sensingcircuit 102, which from examination of FIG. 2 is seen to includecircuitry corresponding to the circuitry of a synchronous Buck switchingregulator circuit, as will be appreciated by those skilled in the art.In a synchronous Buck switching regulator circuit, the diode D shown inthe circuit 104 is replaced with a power switch PS, as is seen to be thecase for input current sensing circuit 102 in which the power switch PS3is contained in place of a diode.

In the embodiment of FIG. 2 the circuitry of the input current sensingcircuit 102 corresponds to the circuitry of a synchronous Buck switchingregulator circuit receiving the duty cycle signal DCYC and the firstsensed voltage V_(IOUT). Note that the first sensed voltage V_(IOUT)provided by the first Buck switching regulator circuit 104 is suppliedto the input current sensing circuit 102 as the input voltage of thesecond Buck switching regulator circuit forming the input currentsensing circuit. By providing the first sensed voltage V_(IOUT) from thefirst Buck switching regulator circuit 104 as the input voltage Vin tothe second Buck switching regulator circuit forming the input currentsensing circuit 102, and by operating the second Buck switchingregulator circuit at the same duty cycle D as the first Buck switchingregulator circuit 104 through the duty cycle signal DCYC, the secondBuck switching regulator circuit generates the second output voltageV_(IIN) having a value proportional to the input current Iin of thefirst Buck switching regulator circuit 104, as will now be explained inmore detail below.

The second Buck switching regulator circuit forming the input currentsensing circuit 102 in essence functions as multiplier to generate thesecond output voltage V_(IIN) having a value proportional to the inputcurrent Iin of the first switching Buck regulator circuit 104. For aconventional Buck switching regulator circuit, the following equationscharacterize the circuit:Vout=D×Vin  (1)D=T _(ON)/(T _(ON) +T _(OFF))=T _(PH-HI)/(T _(PH-HI) +T _(PH-LO))  (2)PIN=Vin×Iin  (2)POUT=Vout×Iout  (3)POUT/PIN=EFF  (4)Iin=Iout×(Vout/Vin)×(1/EFF)  (5)

Equation 1 defines the general relationship between the input voltageVin and output voltage Vout of a Buck switching regulator circuit,namely that the output voltage Vout equals the input voltage Vin timesthe duty cycle D at which the switching regulator circuit is operating.As the equation 2 illustrates, the duty cycle D is defined for thesecond synchronous switching Buck regulator circuit as the timeT_(PH-HI) the phase-high signal PH-HI is active divided by a total cycletime given by the time T_(PH-HI) plus the time T_(PH-LO) the phase-lowsignal PH-LO is active. The efficiency EFF of a Buck switching regulatorcircuit is given by equation 4 and is defined as the output power POUTdivided by the input power PIN. Utilizing equations 2-4 the inputcurrent Iin as a function of output current Iout, output voltage Vout,input voltage Vin and efficiency EFF is given in equation 5. Whileequation 5 does indeed characterize the input current Iin in terms ofthese other measured parameters, the computations required to determinethe value of the input current Iin are relatively complex componentssuch as analog multipliers and dividers, which are also prone tointroducing error into the computation due to component and temperaturevariations, for example.

By utilizing the second Buck switching regulator circuit to form theinput current sensing circuit 102, the computations and circuitryrequired to determine the value of the input current Iin are greatlysimplified. From the above description and equations for conventionalBuck switching regulator circuits, is seen that the second Buckswitching regulator circuit forming the input current sensing circuit102 receives the first sensed voltage V_(IOUT) as the input voltage ofthe regulator circuit. Moreover, referring to the circuitry in regulatorcircuit 204 of FIG. 2 the value of the first sensed voltage V_(IOUT) isgiven by the following equation:VI _(-OUT)=(Iout×RS×A)  (6)

where A is the gain of the amplifier 202.

Now for the second Buck switching regulator circuit forming the inputcurrent sensing circuit 102, from equations 1 and 6 the followingequation for the second output voltage VIIN is found:VIIN=VIOUT×D=(Iout×RS×A)×(Vout/Vin)  (7)

where the duty cycle D of the second Buck switching regulator circuitforming the input current sensing circuit 102 is the same as the dutycycle of the first Buck switching regulator circuit 104 and is thusgiven by Vout/Vin for the first Buck switching regulator circuit.

Now from equation 5 is seen that Iin=Iout×(Vout/Vin)×(1/EFF) or(Vout/Vin)=(Iin×EFF)/Iout, so replacing (Vout/Vin) in equation 7 yields:V _(IIN)=(Iout×RS×A)×((Iin×EFF)/Iout)=Iin×RS×A×EFF  (8)

which shows that the second output voltage V_(IIN) has a value that isproportional to the input current Iin of the first Buck switchingregulator circuit 104.

From equation 8 it is seen that the second Buck switching regulatorcircuit forming the input current sensing circuit 102, when operating atthe same duty cycle D as the first Buck switching regulator circuit 104and when receiving the first sensed voltage V_(IOUT) as an inputvoltage, generates the second output voltage V_(IIN)=Iin×RS×A×EFF. Inthis way, the relatively simple circuitry forming the second Buckswitching regulator circuit of the input current sensing circuit 102generates the second output voltage V_(IIN) having a value that isproportional to the input current Iin of the first Buck switchingregulator circuit 104. As will be appreciated by those skilled in theart, the efficiency EFF term in equation 8 creates an error that can becompensated for in a variety of different ways, such as characterizingthe efficiency of the first Buck switching regulator circuit 104 as afunction of output current Iout and storing this information in thecontrol circuit 200. As previously mentioned, the second output voltageV_(IIN) can be utilized by other circuitry (not shown) to calculate theoverall efficiency EFF of the first Buck switching regulator circuit 104as is desirable in many applications. For example, in battery-poweredapplications external circuitry may monitor the efficiency EFF at whichthe first Buck switching regulator circuit 104 is operating and thencontrol the switching regulator circuit accordingly to conserve batterypower.

Note that although the second Buck switching regulator circuit formingthe input current sensing circuit 102 is shown as including the secondconductor L2, in another embodiment this inductor is omitted and theresistor R7 connected directly to the second phase node PH2. From theabove description and as will be understood by those skilled in the art,where the input current sensing circuit 102 is the second Buck switchingregulator, the circuit functions as a chopping and averaging circuitthat performs a “chopping” and averaging function on the first sensedoutput voltage V_(IOUT) from the first Buck switching regulator circuit104. The synchronous Buck switching regulator circuit is one embodimentof the input current sensing circuit 102 and other types of chopping andaveraging circuits may be utilized to perform the desired function andimplement equation (8), as will be appreciated by those skilled in theart.

FIG. 3 is functional block diagram and schematic of a Buck switchingregulator 100 a including components for implementing the regulatorcircuitry in an integrated circuit according to another embodiment ofthe present invention. The Buck switching regulator 100 a includes aninput current sensing circuit 102 a and first Buck switching regulatorcircuit 104 a that are very similar to the input current sensing circuit102 and first Buck switching regulator circuit 104 in the embodiment ofFIG. 2. Accordingly, like components in the circuits 102 a and 104 ahave been given the same designations as the corresponding components inthe circuits 102 and 104. In the circuit 104 a the filter components R1,R2 and C1 are omitted and amplifier 202 is replaced with atransconductance amplifier 202 a having a capacitor C1 connected acrossits output. Similarly, the only difference between the input currentsensing circuits 102 and 102 a is that in the latter the inductor L2 andresistor R7 are omitted and a transconductance amplifier 208 a iscoupled to drive the output node OUT2 as shown. In this way, resistive,capacitive, and inductive components are eliminated from the first Buckswitching regulator circuit 104 a and the input current sensing circuit102 a to facilitate formation of these circuits in an integratedcircuit. While the operation of components within the circuits 102 a and104 a may vary slightly, such as for the control circuit 200 a, theoperation is substantially the same as previously described withreference to FIG. 2 and thus, for the sake of brevity, will not again bedescribed in detail.

FIG. 4 is a more detailed functional block diagram and schematic of aBuck switching regulator 100 b according to another embodiment of thepresent invention. In the Buck switching regulator 100 b, the inputcurrent sensing circuit 102 b is the same as the circuit 102 of FIG. 2while the first Buck switching regulator circuit 104 b is a synchronousBuck switching regulator circuit including a power switch PS4 in placeof the diode D in the circuit 104 of FIG. 2. Like components in thecircuits 102 b and 104 b have been given the same designations as thecorresponding components in the circuits 102 and 104. In the synchronousBuck switching regulator circuit 104 b, the control circuit 200 bgenerates an upper gate control signal UG to drive the power switch PS1and a lower gate signal to drive the power switch PS4. The UG and LGsignals determine the duty cycle of operation of the circuit 104 b, andare applied are applied to the comparators 204 b and 206 b,respectively, to operate the second Buck switching regulator circuitforming the input current sensing circuit 102 b at the same duty cycle.While the operation of components within the circuits 102 a and 104 cmay vary slightly, such as for the control circuit 200 c, the operationis substantially the same as previously described with reference to FIG.2 and any such slight variations will be appreciated by those skilled inthe art. Thus, for the sake of brevity, the operation of the regulator100 b and components thereof will not be described in more detailherein.

FIG. 5 is functional block diagram and schematic of a charging controlsystem 500 including the Buck switching regulator circuit 104/104 a/104b and input current sensing circuit 102/102 a/102 b of FIGS. 1-4according to another embodiment of the present invention. Only thecircuits 102 and 104 are designated in FIG. 5 and the followingdiscussion will only refer to these particular embodiments although anyembodiments of these circuits may be utilized in the charging systemcontrol system 500.

In the charging control system 500, an adapter power source (not shown)supplies an adapter input voltage V_(AIN) and an adapter input currentI_(AIN) to an adapter input node AIN. This adapter input voltage V_(AIN)and a first portion of the adapter input current I_(AIN) are supplied toelectronic circuitry 502 that is coupled to the adapter input node AINthrough a first sense resistor RS1. The first portion of the adapterinput current I_(AIN) supplied to the electronic circuitry 502 isdesignated a drive input current I_(IN-DR) and in response to thiscurrent flowing through the first sense resistor RS1 an amplifier 504generates a first sensed voltage V_(IN-DR) having a value that isproportional to the value of the drive input current I_(IN-DR) As willbe appreciated by those skilled in the art, the first sense resistor RS1has a suitably small value such that approximately the full value of theadapter input voltage AIN is applied to the electronic circuitry 502, asindicated in FIG. 5. A first capacitor C1 is connected across the inputto the electronic circuitry 502 and functions as a filter of the adapterinput voltage V_(AIN) and current I_(IN-DR).

The Buck switching regulator circuit 104 receives the adapter inputvoltage V_(AIN) and a second portion of the adapter input currentI_(AIN) that is designated a charging input current I_(IN-CH) in FIG. 5.From the adapter input voltage V_(AIN) and charging input currentI_(IN-CH) the Buck switching regulator circuit 104 functions to providea charging output voltage V_(OUT-CH) and charging output currentI_(OUT-CH) on a charging node CH. An energy storage element such as abattery B is coupled to the charging node CH and is recharged throughthe charging output voltage V_(OUT-CH) and charging output currentI_(OUT-CH).

The input current sensing circuit 102 receives the phase signal PHS andcharging output voltage V_(OUT-CH) from the first Buck switchingregulator circuit 104 along with a second sensed voltage V_(IOUT-CH)having a value that is proportional to the charging output currentI_(OUT-CH). Utilizing these signals from the first Buck switchingregulator circuit 104, the input current sensing circuit 102 operates aspreviously described to generate a second output voltage V_(IIN)-CHhaving a value that is proportional to the charging input currentI_(IN-CH) being supplied to the first Buck switching regulator circuit104.

A summation circuit 506 receives the first sensed voltage V_(IN-DR) andsecond output voltage V_(IN-CH) and adds these two voltages to generatea summed voltage signal V_(IAIN) having a value that is proportional tothe adapter input current I_(AIN) being supplied to the charging controlsystem 500 from the adapter power source. The summed voltage signalV_(IAIN) has a value proportional to the adapter input current I_(AIN)because the first sensed voltage V_(IN-DR) indicates the value of thedrive input current I_(IN-DR) and the second output voltage V_(IN-CH)indicates the value of the charging input current I_(IN-CH). The adapterinput current I_(AIN)=I_(IN-CH)+I_(IN-DR) and so the summation of thevoltages V_(IN-CH) and V_(IIN-DR) is the voltage V_(IAIN) having a valueproportional to the adapter input current I_(AIN).

A comparator 508 compares the value of the summed voltage signalV_(IAIN) to a total adapter current threshold V_(IAIN-MAX) and generatesa current limit signal CL in response to the comparison. When the summedvoltage signal V_(IAIN) is less than the threshold V_(IAIN-MAX), thecomparator 508 deactivates the current limit signal CL. In thissituation the sum of the drive input current I_(IN-DR) and charginginput current I_(IN-CH), which equals the adapter input current I_(AIN),is less than some desired maximum value corresponding to the thresholdV_(IAIN-MAX) and thus the charging control system 500 continuesoperating to provide the required power to the electronic circuitry 502and battery B. In contrast, when the summed voltage signal V_(IAIN) isgreater than the threshold V_(IAIN-MAX), the comparator 508 activatesthe current limit signal CL. In this situation the sum of the driveinput current I_(IN-DR) and charging input current I_(IN-CH) is greaterthan the desired maximum value and the operation of the first Buckswitching regulator circuit 104 is adjusted accordingly. Morespecifically, the duty cycle D of the first Buck switching regulatorcircuit 104 is reduced to thereby lower the charging output currentI_(OUT-CH) being supplied to the battery B and the charging inputcurrent I_(IN-CH) being supplied to the first Buck switching regulatorcircuit. More specifically, in response to the current limit signal CL acontrol circuit 200′ in the first Buck switching regulator circuit 104just the duty cycle D of the gating signal G applied to the power switchPS1. The control circuit 200′ is substantially similar to the controlcircuit 200 previously described with reference to FIG. 2 except thatthe control circuit 200′ also operates as just described to control thefirst Buck switching regulator circuit 104 to limit the charging inputcurrent I_(IN-CH) and thereby keep the overall adapter input currentI_(AIN) less than a desired maximum value corresponding to the totaladapter current threshold V_(IAIN-MAX).

The charging control system 500 operates to ensure that the requireddrive input current I_(IN-DR) is supplied to the electronic circuitry502 while also ensuring that the adapter input current I_(AIN) beingprovided by the adapter power source (not shown) does not exceed amaximum value. In this way, as the drive input current I_(IN-DR)required by the electronic circuitry 502 varies, the control system 500adjust the charging output current I_(OUT-CH) supplied to the battery Bto charge the battery as quickly as possible. For example, when theelectronic circuitry 502 corresponds to computer circuitry in a laptopcomputer, the drive input current I_(IN-DR) will vary depending upon theprocessing requirements of the electronic circuitry. During periods oflow I_(IN-DR) requirements, the control system 500 enables the firstBuck switching regulator circuit 104 to provide a higher charging outputcurrent I_(OUT-CH) to thereby charge the battery B more quickly.Conversely, during periods of high I_(IN-DR) requirements, such as whenthe computer circuitry is operating a processor intensive applicationlike voice recognition software, the control system 500 reduces thecharging input current I_(IN-CH) to maintain the adapter input currentI_(AIN) less than the threshold or maximum value.

FIG. 6 is a functional block diagram of an electronic system 600including the switching regulator 100/100 a/100 b of FIGS. 1-4 and/orthe charging control system 500 of FIG. 5 according to anotherembodiment of the present invention. The electronic system 600 includeselectronic circuitry 602 including the switching regulator 100/100 a/100b and/or the charging control system 500. The electronic circuitry 602may be a variety of different types of circuitry depending upon theparticular application for which the 100/100 a/100 b and/or the chargingcontrol system 500 is being utilized. For example, in one embodiment theelectronic circuitry 602 corresponds to computer circuitry in a laptopcomputer or other type of portable electronic device. In such systems,an energy storage element 604, such as a rechargeable battery, may becoupled to the electronic circuitry 602 and switching regulator 100/100a/100 b and/or charging control system 500 to thereby charge the energystorage element. The system 600 may further include interface devices606 that may take a variety of different forms, such as an LCD screenand an alphanumeric keypad, which function to allow a user to interfacewith the system.

Even though various embodiments and advantages of the present inventionhave been set forth in the foregoing description, the above disclosureis illustrative only, and changes may be made in detail and yet remainwithin the broad principles of the present invention. Moreover, thefunctions performed by the elements illustrated and described withreference to FIGS. 1-5 may in some instances be combined and performedby fewer elements, separated and performed by more elements, or combinedinto different functional blocks depending upon the actual componentsused and system being designed, as will be appreciated by those skilledin the art. Therefore, the present invention is to be limited only bythe appended claims.

What is claimed:
 1. A Buck switching regulator, comprising: first Buckswitching regulator circuitry operable in response to a second outputvoltage to generate a first output voltage from an input voltage andoperable to generate a first sensed voltage having a value that isproportional to an output current being provided by the first Buckswitching regulator circuitry, and the first Buck switching regulatorcircuitry receiving an input current and operating at a first duty cycledetermined by a duty cycle signal; and input current sensing circuitryincluding second Buck switching regulator circuitry coupled to the firstBuck regulator switching circuitry to receive the duty cycle signal andto receive the first sensed voltage as an input voltage to the secondBuck switching regulator circuitry, the second Buck switching regulatorcircuitry operable responsive to the duty cycle signal to generate thesecond output voltage from the first sensed voltage, the second outputvoltage having a value that is proportional to the input current beingsupplied to the first Buck switching regulator circuitry.
 2. The Buckswitching regulator of claim 1, wherein the first Buck switchingregulator circuitry includes a first power switch and a diode coupled inseries between an input source providing the input voltage and areference voltage source, the anode of the diode being coupled to thereference voltage source and a first phase node being defined at theinterconnection of the cathode of the diode and the power switch; andwherein the duty cycle signal includes a phase signal on the first phasenode and the first output voltage on a first output node of the firstBuck switching regulator circuitry.
 3. The Buck switching regulator ofclaim 2 wherein the input current sensing circuitry comprises: a firstcomparator having a first input coupled to the first phase node and asecond input coupled to the output node, the first comparator operableto generate a phase-high signal on an output responsive to signals onthe phase and output nodes; a second comparator having a first inputcoupled to the output node and a second input coupled to the first phasenode, the second comparator operable to generate a phase-low signal onan output responsive to signals on the first phase and output nodes; afirst power switch having a control input coupled to the output of thefirst comparator to receive the phase-high signal and having a firstsignal node coupled to receive the first sensed voltage, and having asecond signal node; a second power switch having a control input coupledto the output of the second comparator to receive the phase-low signaland a first signal node adapted to receive a reference voltage, and thesecond power switch having second signal node coupled to the secondsignal node of the first power switch to define a second phase node; andan output filter coupled to the second phase node and operable to filtera signal on the second phase node to generate the second output voltage.4. The Buck switching regulator of claim 3 wherein the output filtercomprises a transconductance amplifier.
 5. The Buck switching regulatorof claim 3 further comprising a first inductive element coupled betweenthe second phase node and the output filter.
 6. The Buck switchingregulator of claim 3 wherein the first Buck switching regulatorcircuitry further comprises: an inductive element coupled in series withan output sense resistive element between the first phase node and theoutput node of the first Buck switching regulator circuitry; and adifferential amplifier having a first input coupled to the output nodeand a second input coupled to a node defined by the interconnection ofthe inductive element and the output sense resistive element, thedifferential amplifier operable to generate the first sensed voltageresponsive a voltage across the output sense resistive element.
 7. TheBuck switching regulator of claim 6 wherein the second inductive elementcomprises a single inductor.
 8. The Buck switching regulator of claim 6wherein the first Buck switching regulator circuitry further comprisescontrol circuitry operable to control the operation of the first Buckswitching regulator circuitry utilizing the first sensed voltage, secondoutput voltage, the input voltage, and the first output voltage.
 9. TheBuck switching regulator of claim 1, wherein the first Buck switchingregulator circuitry comprises a synchronous Buck regulator circuitincluding a high-side power switch and low-side power switch couple inseries between an input source providing the input voltage and areference voltage source, the high-side power switch receiving aphase-high signal and the low-side power switch receive a phase-lowsignal; and wherein the duty cycle signal comprises the phase-high andphase-low signals.
 10. A charging system, comprising: an adapter inputnode adapted to receive an adapter input voltage and adapter inputcurrent and adapted to be coupled to electronic circuitry; a firstvoltage sensing circuit coupled to the power adapter input node andoperable to sense a drive input current being supplied to the electroniccircuitry and to generate a first sensed voltage having a valueindicating the value of the drive input current; first Buck switchingregulator circuitry coupled to the power adapter input node and to acharging node adapted to be coupled to an energy storage element, thefirst Buck switching regulator circuitry operable to generate a chargingoutput voltage on the charging node and to generate a second sensedvoltage having a value that is proportional to a charging output currentbeing provided by the first Buck switching regulator circuitry, and thefirst Buck switching regulator circuitry receiving a charging inputcurrent from the adapter input node and including control circuitryoperable to control the first Buck switching regulator circuitry tooperate at a first duty cycle and to adjust the duty cycle responsive toa current limit signal; input current sensing circuitry including secondBuck switching regulator circuitry coupled to the first Buck regulatorswitching circuitry to receive the duty cycle signal and to receive thesecond sensed voltage as an input voltage to the second Buck switchingregulator circuitry, the second Buck switching regulator circuitryoperable responsive to the duty cycle signal to generate a second outputvoltage from the second sensed voltage, the second output voltage havinga value that is proportional to the charging input current beingsupplied to the first Buck switching regulator circuitry; a summationcircuit coupled to the first voltage sensing circuit to receive thefirst sensed voltage having a value indicating the value of the driveinput current and coupled to the input current sensing circuitry toreceive the second output voltage having a value proportional to thecharging output current, the summation circuit operable to sum the firstsensed voltage and second output voltage to generate a total adaptercurrent signal; and a comparison circuit coupled to the summationcircuit and to the control circuitry in the first Buck switchingregulator circuitry, the comparison circuit operable to compare thetotal adapter current signal to a total adapter current threshold andgenerate the current limit signal responsive to this comparison.
 11. Thecharging system of claim 10 wherein the comparison circuit activates thecurrent limit signal responsive to the total adapter current signalbeing equal to or greater than the total adapter current threshold andresponsive to the active current limit signal the control circuit in thefirst Buck switching regulator circuitry adjusts the duty cycle signalto reduce the value of the charging output current.
 12. The chargingsystem of claim 10 wherein a rechargeable battery is coupled to thecharging node.
 13. The charging system of claim 10, wherein the firstBuck switching regulator circuitry includes a first power switch and adiode coupled in series between the power adapter input node and areference voltage source, the anode of the diode being coupled to thereference voltage source and a phase node being defined at theinterconnection of the cathode of the diode and the power switch; andwherein the duty cycle signal includes a phase signal on the phase nodeand the charging output voltage on the charging node.
 14. The chargingsystem claim 13 wherein the input current sensing circuitry comprises: afirst comparator having a first input coupled to the phase node and asecond input coupled to the charging node, the first comparator operableto generate a phase-high signal on an output responsive to signals onthe phase and charging nodes; a second comparator having a first inputcoupled to the charging node and a second input coupled to the phasenode, the second comparator operable to generate a phase-low signal onan output responsive to signals on the phase and charging nodes; a firstpower switch having a control input coupled to the output of the firstcomparator to receive the phase-high signal and a first signal nodecoupled to receive the second sensed voltage, and having a second signalnode; a second power switch having a control input coupled to the outputof the second comparator to receive the phase-low signal and a firstsignal node adapted to receive a reference voltage, and the second powerswitch having second signal node coupled to the second signal node ofthe first power switch to define a second phase node; and an outputfilter coupled to the second phase node and operable to filter a signalon the second phase node to generate the second output voltage.
 15. Anelectronic system, comprising: electronic circuitry including a Buckswitching regulator, the Buck switching regulator including, first Buckswitching regulator circuitry operable in response to a second outputvoltage to generate a first output voltage from a first input voltageand operable to generate a sensed current output voltage having a valuethat is proportional to an output current being provided by the firstBuck switching regulator circuitry, the first Buck switching regulatorcircuitry configured to provide the first output voltage and the outputcurrent to a load to thereby supply power to the load, and the firstBuck switching regulator circuitry receiving an input current andoperating at a first duty cycle determined by a duty cycle signal; andinput current sensing circuitry including second Buck switchingregulator circuitry coupled to the first Buck regulator switchingcircuitry to receive the duty cycle signal and to receive the sensedcurrent output voltage as an input voltage to the second Buck switchingregulator circuitry, the second Buck switching regulator circuitryoperable responsive to the duty cycle signal to generate the secondoutput voltage from the sensed output voltage, the second output voltagehaving a value that is proportional to the input current being suppliedto the first Buck switching regulator circuitry; and at least oneinterface device coupled to the electronic circuitry.
 16. The electronicsystem of claim 15 wherein the electronic circuitry comprises laptopcomputer circuitry.
 17. The electronic system of claim 15, wherein thesystem further comprises an energy storage element coupled to thecomputer circuitry; and wherein the computer circuitry further includesa charging system, the charging system including, a power adapter inputnode adapted to receive an adapter input voltage and adapter inputcurrent from an adapter power source; a first voltage sensing circuitcoupled to the power adapter input node and operable to sense a driveinput current being supplied to the computer circuitry and to generate afirst sensed voltage having a value indicating the value of the driveinput current; the first Buck switching regulator circuitry; the inputcurrent sensing circuitry; a summation circuit coupled to the firstvoltage sensing circuit to receive the first sensed voltage and coupledto the input current sensing circuitry to receive a second outputvoltage having a value proportional to a charging current being suppliedto the first Buck switching regulator, the summation circuit operable tosum the first sensed voltage and second output voltage to generate atotal adapter current signal; and a comparison circuit coupled to thesummation circuit and to control circuitry in the first Buck switchingregulator circuitry, the comparison circuit operable to compare thetotal adapter current signal to a total adapter current threshold andgenerate a current limit signal responsive to this comparison, thecontrol circuitry in the first Buck switching regulator circuitryoperable to operate the first Buck switching regulator circuitry at afirst duty cycle and to adjust the duty cycle signal responsive to thecurrent limit signal.
 18. A method of sensing the input current beingsupplied to a first Buck switching regulator, the method comprising:controlling the first Buck switching regulator at a first duty cycle togenerate a first voltage having a value indicating the value of anoutput current being provided by the first Buck switching regulator;providing the first voltage as an input voltage to a second Buckswitching regulator; controlling the second Buck switching regulator atthe first duty cycle to generate a second output voltage, the secondoutput voltage having a value that is proportional to the value of theinput current being supplied to the first Buck switching regulator; andcontrolling the first Buck switching regulator in response to the secondoutput voltage.
 19. The method of claim 18 wherein controlling thesecond Buck switching regulator at the first duty cycle comprisesgenerating duty cycle signals responsive to a phase voltage on a phasenode in the first Buck switching regulator and an output voltage on anoutput node of the first Buck switching regulator.
 20. The method ofclaim 18, wherein controlling the first Buck switching regulator at thefirst duty cycle comprises generating phase-high and phase-low signals;and wherein controlling the second Buck switching regulator at the firstduty cycle comprises providing the phase-high and phase-low signals tocontrol operation of the second Buck switching regulator.
 21. The methodof claim 18 wherein controlling the first Buck switching regulator atthe first duty cycle to generate the first voltage comprises: sensingthe output current from the first Buck switching regulator; andgenerating the first voltage responsive to the sensed output current.22. The method of claim 21 wherein sensing the output current from thefirst Buck switching regulator and generating the first voltageresponsive to the sensed output current comprise supplying the outputcurrent through a resistive element to thereby sense the output currentand generate the first voltage.
 23. The method of claim 18, whereincontrolling the second Buck switching regulator includes supplying acurrent through an inductive element of the second Buck switchingregulator.
 24. The charging system of claim 14 further comprising afirst inductive element coupled between the second phase node and theoutput filter.
 25. The electronic system of claim 15, wherein the inputcurrent sensing circuitry comprises: a first comparator having a firstinput coupled to the first phase node and a second input coupled to theoutput node, the first comparator operable to generate a phase-highsignal on an output responsive to signals on the phase and output nodes;a second comparator having a first input coupled to the output node anda second input coupled to the first phase node, the second comparatoroperable to generate a phase-low signal on an output responsive tosignals on the first phase and output nodes; a first power switch havinga control input coupled to the output of the first comparator to receivethe phase-high signal and having a first signal node coupled to receivethe first sensed voltage, and having a second signal node; a secondpower switch having a control input coupled to the output of the secondcomparator to receive the phase-low signal and a first signal nodeadapted to receive a reference voltage, and the second power switchhaving second signal node coupled to the second signal node of the firstpower switch to define a second phase node; and an output filter coupledto the second phase node and operable to filter a signal on the secondphase node to generate the second output voltage.
 26. The electronicsystem of claim 25 further comprising a first inductive element coupledbetween the second phase node and the output filter.
 27. A Buckswitching regulator, comprising: a Buck switching regulator circuitoperable responsive to a second output voltage to generate a firstoutput voltage from an input voltage and operable to generate a firstsensed voltage having a value that is proportional to an inductorcurrent of the Buck switching regulator circuit, and the Buck switchingregulator circuit receiving an input current and operating at a firstduty cycle determined by a duty cycle signal; and an input currentsensing circuit coupled to the Buck switching regulator circuit toreceive the first sensed voltage and the duty cycle signal and operableresponsive to the first sensed voltage and the duty cycle signal togenerate the second output voltage having a value that is proportionalto the input current being supplied to the Buck switching regulatorcircuit.
 28. The Buck switching regulator circuit of claim 27, whereinthe input current sensing circuit comprises a chopping and averagingcircuit.
 29. The Buck switching regulator circuit of claim 28, whereinthe chopping and averaging circuit comprises a Buck regulator circuit.